Vehicles may include a coolant systems configured to reduce overheating of an engine by transferring the heat to ambient air. Therein, coolant is circulated through the engine block to remove heat from the hot engine, and the heated coolant is then circulated through a radiator near the front of the vehicle. Heated coolant may also be circulated through a heat exchanger to heat a passenger compartment. The coolant system may include various components such as various valves, pumps, and one or more thermostats. In the event of a cooling system degradation due to component malfunction (e.g., water pump degradation), or due to loss of coolant from the cooling system (e.g., due to a coolant leak), the engine may overheat. Engine overheating may be exacerbated in turbocharged direct injected engines which tend to run hotter due to boost and higher loads.
Various approaches have been developed to address engine overheating in the event of coolant system degradation. One example approach, shown by Willard et al. in U.S. Pat. No. 9,217,379, addresses engine overheating by alternately shutting down fuel to one or more cylinders while maintaining vehicle torque demand with the fueled cylinders. Cylinder cooling is achieved as cool un-combusted air flows through the unfueled cylinders. By shutting off fuel on an individual cylinder basis, flexibility in cooling and torque control is provided. In still other approaches, cylinder fueling may be shut off on a bank-wise basis to cool the deactivated bank, while the active bank continues to generate torque for vehicle propulsion.
The inventors herein have recognized potential issues with the above approach. As one example, in engines configured with start-stop capabilities, even with all cylinders deactivated, under-hood temperatures may continue to climb. Due to the vehicle being static and not moving, even if additional cooling fans are activated, the idle-stopped engine may continue to overheat. If the engine is restarted to increase cooling air flow, the fuel economy benefit associated with the start-stop operation may be lost. Likewise, in a hybrid electric vehicle, pulling up a shutdown engine (by transitioning out of an electric-only mode) to flow cool air through the overheated engine may result in a net fuel penalty.
The inventors herein have developed systems and methods to at least partially address the above issues. In one example, a method for cooling an overheated engine includes while engine temperature is greater than a threshold temperature and when engine idle-stop conditions are met, spinning an engine unfueled and operating an electrical intake air compressor to route air to engine cylinders via a charge air cooler. In this way, engine cooling can be expedited without needing to restart the engine.
As one example, a boosted engine may be configured with an intake compressor coupled to an electric motor. The electric intake compressor may be included in an electric turbocharger, or may be coupled to a mechanical turbocharger, downstream of a turbine-drive intake compressor. Responsive to engine idle-stop conditions being met, engine fueling may be disabled. In addition, engine temperature may be assessed. Responsive to a higher than threshold engine temperature, or a higher than threshold rate of rise in engine temperature, an engine controller may spin the engine unfueled (such as via a starter motor, or a hybrid driveline electric motor), while also enabling the electric intake compressor. Therein, a pulse-width commanded to the electric motor driving the electric intake compressor may be increased as the degree of engine cooling required increases. As a result of compressor operation intake air, drawn in via the spinning engine, may be delivered to engine cylinders after being cooled upon passage through a charge air cooler. Once the engine is sufficiently cooled, the electric intake compressor may be disabled and the engine may be spun to, and maintained at, rest until engine restart conditions are met. In one example, the electric intake compressor operation may be performed while existing coolant system fans are operated to expedite the cooling. In still further examples, responsive to engine overheating while a hybrid electric vehicle is operated in an engine-only or an assist mode, the vehicle may be temporarily transitioned to an electric-only mode, and operation of the electric intake compressor may be coordinated with the unfueled spinning of the engine to lower the engine temperature. Thereafter, engine operation may be resumed.
In this way, engine overheating may be quickly addressed without requiring an engine to be pulled up for cooling purposes. By spinning an engine unfueled, air can be drawn into the engine cylinders. By concurrently spinning an intake compressor via an electric motor, compressed air can be cooled upon passage through a charge air cooler before it is delivered to the cylinders. The technical effect of flowing cooled, compressed air through the cylinders is that heat loss from cylinder walls and pistons can be expedited, reducing engine and under-hood temperature rise. By operating the electric intake compressor alongside a cooling fan, engine temperatures may be maintained within a target range even when the engine is shutdown. By expediting engine cooling during conditions when an engine is shutdown, such as during an idle-stop, engine restarts responsive to engine overheating can be reduced, prolonging the duration and fuel economy benefits of an engine idle-stop.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.